The present invention relates to platens for heat sealing film to the lip of a cup, a method of heat sealing film, and a cup formed by the heat sealing method.
Platens and methods for heat sealing film to the lip of a cup are known, as are cups with pieces of heat sealable film fused to their lips over their open ends. U.S. Pat. No. 4,050,971 (the content whereof is incorporated herein by reference) describes a device and method for sealing a piece of film over the end of a cup. The device described therein includes a heat sealing platen comprising a heat conductive rigid support member, a layer of resiliently elastic material overlaying the support member and having an annular outer surface adapted to press and conform film against the lip of the cup, and means for heating to provide a temperature at the annular outer surface of the elastic material adapted to seal film to the lip of the cup. The device forms sealed cups by positioning a piece of film adjacent the lip of the cup and over the cup opening, and pressing the film into contact with the lip of the cup while heating the film sufficiently to fuse it to the lip.
Additionally U.S. Pat. No. 4,087,181 describes a novel structure for forming perforations around a small portion of a piece of film applied to a cup by a device such as that described in U.S. Pat. No. 4,050,971, which small portion of the film can be removed to provide a straw-hole through the film. While this small portion of the film can be easily punched out so that a straw can be inserted into the cup, it has been found that the perforations are not easily seen by users of the cup, so that too many users of such cups unnecessarily resort to peeling the film away to gain access to the cup.
Attempts have been made to alert users by providing instructions in the film, however it is impossible to localize such instructions around the perforations since there is no way to tell where the perforations will be made in the film at the time that the film is printed.